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Interpretive Summary: Previous studies by ARS and University of Florida scientists at Gainesville, FL showed that Maverick soybean in a polycarbonate greenhouse grew tall and produced long internodes. They found that polycarbonate transmitted no ultraviolet (UV) radiation; specifically, no UV-B and no UV-A wavelengths. However, a glass greenhouses transmitted about 50% of UV-A. A follow-up study was conducted on Maverick and Williams-82 soybean in a polycarbonate greenhouse, a glass greenhouse, and outdoors (during daytime) to determine the effect of (i) exclusion of both UV-B and UV-A, (ii) exclusion of UV-B only, and (iii) exposure to natural solar UV for 8 hours daily. Both greenhouses and were maintained at day/night temperatures of 30/22 degrees C (86/71.6 degrees F). These ARS and University of Florida scientists found that the average mainstem length was 53, 78, and 167 cm (21, 31, and 66 inches) for natural sunlight, excluded UV-A radiation, and excluded UV-B and UV-A radiation, respectively. The average number of nodes was 14.4, 16.0, and 17.2 for natural sunlight, excluded UV-A radiation, and excluded UV-B and UV-A radiation, respectively. Pod yield tended to increase with UV exclusion, but effects were not pronounced. Materials should be carefully selected for transmission characteristics of UV radiation for research (or commercial production) of plants sensitive to UV exclusion, such as soybean, other grain legumes, and lettuce.

Technical Abstract: Soybean [Glycine max (L.) Merr.] cultivars Williams-82 and Maverick were grown in a polycarbonate greenhouse, a glass greenhouse, and outdoors (during daytime) to investigate the effect of (i) exclusion of both solar UV-B radiation (280-320 nm) and UV-A radiation (320-400 nm), (ii) exclusion of solar UV-B radiation only, and (iii) exposure to natural solar UV radiation during daytime conditions (09:00 to 17:00 h daily). Both the polycarbonate greenhouse and the glass greenhouse were maintained at day/night air temperatures of 30/22 °C. The purpose of the research was to quantify the growth differences due to partial and total UV exclusion in comparison with exposure to natural daytime UV radiation. The main finding was that the exclusion of both solar UV-B and UV-A radiation caused elongated internodes on the soybean plants which resulted in greater plant height. The mean mainstem lengths of Williams-82 were 50, 73, and 169 cm for direct solar UV radiation, excluded UV-A radiation only, and both excluded UV-B and UV-A radiation, respectively. Similarly, the mean mainstem lengths of Maverick were 55, 84, and 165 cm for full daytime UV radiation, excluded UV-A radiation only, and both excluded UV-B and UV-A radiation, respectively. There also was a slight increase in the number of nodes with increasing extent of UV radiation exclusion. The mean final numbers of nodes (V-stage) of Williams-82 were 14.2, 15.7, and 16.7 for full daytime UV radiation, excluded UV-A radiation only, and both excluded UV-B and UV-A radiation, respectively. Likewise, the mean final numbers of nodes of Maverick were 14.5, 16.2, and 17.7 for full daytime UV radiation, excluded UV-A radiation only, and both excluded UV-B and UV-A radiation, respectively. For the Maverick cultivar, pod yield was greater with elongated internodes and more internodes associated with exclusion of both UV-B and UV-A, but this effect was not as clear for the Williams-82 cultivar. Finally, spectral transmission of greenhouse or controlled environment covering material and UV radiation conditions should be considered for research on (or commercial production of) plants that are sensitive to UV exclusion, such as other grain legumes and lettuce.